JPS6367237B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flame detector that detects a fire by detecting ultraviolet rays emitted from flames when a fire occurs.

Conventionally, this type of ultraviolet flame detector has a discharge tube 1 that detects ultraviolet light and discharges it, a booster circuit 2 that applies high voltage to the discharge tube, and a pulse of a constant width that outputs the output of the discharge tube 1, as shown in Figure 1. It is composed of a one-shot multi-circuit 3 that converts the voltage into a single shot, an integrating circuit section 4 that has a function of charging and discharging the capacitor C to prevent malfunctions due to dark discharge, a level detection circuit 5 that detects the voltage of the capacitor C, and a switching circuit 6. has been done. In this circuit, discharging begins immediately after charging as shown in Figure 2, so if the pulse output of the one-shot multi circuit 3 is coarse, the detector may not operate, or even if it operates, the pulse output There were variations in operating time due to the difference in the interval between occurrences.

In view of the above problems, an object of the present invention is to obtain a flame detector with stable operation time.

The following explanation will be given with reference to FIGS. 3 and 4, in which the same parts as in the conventional example are given the same reference numerals. A discharge tube 1 that detects and discharges ultraviolet light is connected to a power line, and a high voltage is applied to the discharge tube. Connected via booster circuit 2. This booster circuit 2 is composed of, for example, a multistage rectifier circuit and a blocking oscillation circuit. At both ends of the output resistor of the discharge tube 1, there are provided a first one-shot multi-circuit 3a that converts the output into a pulse width serving as a reference for operating time, and a second one-shot multi-circuit 3a that converts the output into a pulse width smaller than the pulse width. Yotsuto multi circuit 3b
are connected in parallel via the integrating circuit section 4. This integrating circuit section 4 is a second one-shot multi-circuit 3b.
Diode D ₁ is connected in the forward direction from the first one-shot multi-circuit 3a, diode D ₂ is connected in the reverse direction from the first one-shot multi-circuit 3a, and the resistor R ₁ that sets the charging time constant is connected to the diode D ₁ , and the discharge voltage is connected to the diode D ₂ . Connect a resistor _R2 that determines the time constant, and connect a capacitor C to this. Therefore, the resistor R ₂ can be made small to ensure quick discharge. Furthermore, a level detection circuit 5 for detecting whether the voltage across the capacitor C has reached a predetermined level, and a switching circuit 6 for outputting a switch output for driving an alarm using a signal from the level detection circuit are connected.

Next, to explain the operation of the present invention, in FIG. 4, when the first ultraviolet ray emitted from the flame enters the discharge tube 1, a needle-like pulse is emitted from the discharge tube 1, and the first
The second one-shot multi-circuit 3a generates an output with a pulse width Ta serving as a reference for operating time, and the second one-shot multi-circuit 3b generates an output with a pulse width Tb. This pulse is passed through diode D ₁ and resistor R ₁
The capacitor C is charged through the system. Here the first
During the time that the one-shot multi-circuit 3a is outputting the pulse, discharge in the path of the resistor R ₂ and the diode D ₂ is blocked. When ultraviolet rays enter the discharge tube 1 successively, charging is performed continuously as shown in the level of the integrating circuit section 4 by pulses generated from the second one-shot multi-circuit 3b. When a predetermined number of pulses having a pulse width Tb are generated within the time period having the pulse width Ta, the level detection circuit 5 detects this and activates the switching circuit 6. Also, the pulse width
If a predetermined number of outputs from the one-shot multi-circuit 3b are not generated within the time Ta, the switching circuit 6 will not operate, and the charge will be immediately discharged through the resistor R ₂ , the diode D ₂ , and the one-shot multi-circuit 3 a, and the circuit will be discharged again. It will be charged from the beginning.

As described above, in an ultraviolet flame detector using an ultraviolet detection discharge tube, there is a first one-shot multi-circuit that converts the pulse output of the discharge tube into a pulse for setting an operating time of a constant width, and A second one-shot multi-circuit that converts the pulse width into a short pulse width is connected to the output side of the discharge tube. This ultraviolet flame detector is characterized by connecting both multi-circuits to a capacitor through a capacitor, and detecting the voltage of the capacitor with a level detection circuit to obtain a switching output. While the first one-shot multi-circuit is outputting pulses due to the first discharge, the pulse output of the second one-shot multi-circuit due to subsequent discharges continues to be stored in the capacitor and is not discharged. Therefore, the detector operates only when the second one-shot multi-circuit outputs a predetermined number of pulses, and a detector with stable operating sensitivity can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional example, FIG. 2 is an output state diagram of the conventional example, FIG. 3 is a circuit diagram of the present invention, and FIG. 4 is an output state diagram of the present invention. 1... Discharge tube, 2... Boost circuit, 3a, 3b...
...one-shot multi-circuit, 5...level detection circuit, 6...switching circuit, _D1 , _D2 ...diode, C...capacitor.

Claims (1)

[Claims] 1. In an ultraviolet flame detector using an ultraviolet detection discharge tube, a first one-shot multi-circuit converts the pulse output of the discharge tube into a pulse for setting an operating time of a constant width, and a pulse width shorter than that of the circuit. A second one-shot multi-circuit to be converted is connected to the output side of the discharge tube, and the first multi-circuit connects both multi-circuits via a backward-connected diode, and the second multi-circuit connects both multi-circuits via a forward-connected diode. An ultraviolet flame detector characterized in that the voltage of the capacitor is detected by a level detection circuit to obtain a switching output.